What distinctive feature is common in Bourbon whiskey?

Bourbon whiskey is defined by several key characteristics, one of which is that it must be aged in new charred oak barrels. This requirement is crucial in developing the bourbon's flavor profile, as the charring process caramelizes the wood sugars, imparting flavors such as vanilla, caramel, and toasted oak. The aging process in these barrels enhances the smoothness and complexity of the whiskey, which is a fundamental aspect of bourbon production. This distinctive feature sets bourbon apart from other types of whiskey, which may use reused barrels or different types of barrels entirely.

The other options do not align with the defining characteristics of bourbon. For example, bourbon is not primarily made from malted barley; instead, it must contain at least 51% corn in its mash bill. Additionally, bourbon is uniquely American and cannot be produced in Scotland, which is known for Scotch whisky. Lastly, while there are flavored whiskeys available on the market, traditional bourbon does not include added flavors like fruits—it retains its distinct character through the aging process in the charred oak barrels.